Krivosudský Lukáš, Schwendt Peter, Šimunek Ján, Gyepes Róbert
Department of Inorganic Chemistry, Comenius University, Faculty of Natural Sciences, Mlynská dolina, 842 15 Bratislava, Slovakia.
Department of Inorganic Chemistry, Comenius University, Faculty of Natural Sciences, Mlynská dolina, 842 15 Bratislava, Slovakia.
J Inorg Biochem. 2015 Jun;147:65-70. doi: 10.1016/j.jinorgbio.2015.01.011. Epub 2015 Jan 24.
The structures of two stereoisomers of the chiral anion VO2(N-salicylidene-isoleucinato) possessing three centers of chirality, the vanadium atom (configuration A/C) and the isoleucine moiety (configuration R/S on alpha and beta carbons), are presented. The absolute configuration of all available stereosiomers, CSS, ARR, CSR and ARS, was determined by electronic circular dichroism (ECD), which allows distinguishing between diastereomers, and by vibrational circular dichroism (VCD) capable of differentiating between all four stereoisomers. The comparison of experimental VCD and infrared (IR) spectra with simulated spectra for band assignment revealed the IR spectra of the diastereomers differing significantly in the CH stretching region of the aromatic part in the molecule. Crystallization from binary systems composed of equal ratio of two stereoisomers of isoleucine, unveiled the lower solubility of CSS and ARR stereoisomers, while a longer crystallization time of the CSR and ARS stereoisomers allowed proceeding the vanadium-catalyzed epimerization, leading to the subsequent presence of the CSS and ARR stereoisomers in the product obtained.
本文展示了手性阴离子VO2(N-水杨醛异亮氨酸酯)的两种立体异构体的结构，该阴离子具有三个手性中心，即钒原子（构型A/C）和异亮氨酸部分（α和β碳原子上的构型R/S）。通过电子圆二色光谱（ECD，可区分非对映异构体）和振动圆二色光谱（VCD，能够区分所有四种立体异构体）确定了所有可用立体异构体CSS、ARR、CSR和ARS的绝对构型。将实验VCD光谱和红外（IR）光谱与用于谱带归属的模拟光谱进行比较，结果表明非对映异构体的IR光谱在分子芳香部分的CH伸缩区域存在显著差异。由等比例的两种异亮氨酸立体异构体组成的二元体系结晶实验表明，CSS和ARR立体异构体的溶解度较低，而CSR和ARS立体异构体的结晶时间较长，这使得钒催化的差向异构化得以进行，从而导致在所得产物中随后出现CSS和ARR立体异构体。
